Apparatus for eliminating condensation from the outer walls of refrigeration enclosures



y ,1969 M. u. SCHWEIGER 3,443,395

APPARATUS FOR ELIMINATING CONDENSATION FROM THE OUTER WALLS OF REFRIGERATION ENCLOSURES Filed Nov. 16, 1967 FIQI. .3

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United States Patent 3,443,395 APPARATUS FOR ELIMINATING CONDENSATION FROM THE OUTER WALLS OF REFRIGERATION ENCLOSURES Manfred U. Schweiger, Versailles, Ky., assignor to Texas Instruments Incorporated, Dallas, Tex., a corporation of Delaware Filed Nov. 16, 1967, Ser. No. 683,554 Int. Cl. F25d 21/08 US. Cl. 62-140 9 Claims ABSTRACT OF THE DISCLOSURE Apparatus is disclosed for automatically energizing socalled anti-sweat heaters which heat the outer wall of a refrigerator to eliminate therefrom condensation which would otherwise be caused by cooling of the outer wall due to heat leakage or transfer through the refrigerator insulation. The apparatus includes a semiconductor current switching device such as an SCR for controlling the flow of electric current to the heater. A condensation sensor is provided which includes a pair of electrodes bridged by an insulating surface. The sensor is positioned so as to be cooled with the outer wall of the refrigerator. Further means are provided for energizing the semiconductor current switching device when the resistance between the sensor electrodes falls below a predetermined level. Accordingly, when the resistance between the electrodes is reduced by the condensation of moisture on the insulating surface between them, the heater is energized by the semiconductor current switching device thereby eliminating condensation from the outer wall.

This invention relates to refrigeration systems and more particularly to apparatus for eliminating condensation on the outer walls of a refrigeration enclosure.

In domestic refrigeration systems such as refrigerators and freezers, it is undesirable to permit condensation to form on the outer wall of the refrigeration enclosure or cabinet. In a high humidity environment such condensation forms when the outer wall is cooled by heat transfer or leakage through the enclosure walls and gives the enclosure the appearance of sweating. In some refrigerators and freezers sold commercially, so-called anti-sweat heaters are provided for heating the outer wall of the enclosure or cabinet. These heaters are typically operated either continuously or under manual control to eliminate condensation from the outer wall of the enclosure. Continuous operation of such heaters is, however, wasteful of electricity and increases the cost of operation while manual control is often neglected or brought into play only after a problem has occurred.

Among the several objects of the present invention may be noted the provision of apparatus for automatically energizing anti-sweat heaters in refrigeration apparatus; the provision of such apparatus which energizes the heaters substantially only when needed; the provision of such apparatus which is relatively eflicient; the provision of such apparatus which is reliable; and the provision of such apparatus which is relatively simple and inexpensive.

Briefly, apparatus according to this invention is useful in a refrigeration system including an enclosure having inner and outer walls separated by an insulating layer, means for cooling a space within the enclosure, and electric heater means for heating the outer wall to eliminate therefrom condensation caused by cooling of the outer wall due to heat transfer through the insulating layer. The apparatus includes semiconductor current switching means for controlling the flow of electric current to the heater means and includes also sensor means having a Patented May 13, 1969 pair of electrodes which are bridged by an electrically insulating surface. The sensor means is positioned relative to the enclosure so as to be cooled with the outer wall thereof. Means are further provided for energizing the semiconductor current switching means when the resistance between the sensor electrodes falls below a predetermined level. Accordingly, when the resistance between the electrodes is reduced by condensation of moisture on the insulating surface therebetween, the heater means is energized by the semiconductor switching means and eliminates condensation from the outer wall.

The invention accordingly comprises the constructions hereinafter described, the scope of the invention being indicated in the following claims.

In the accompanying drawings in which one of various possible embodiments of the invention is illustrated:

FIG. 1 is a view in section of a portion of a refrigeration enclosure which is provided with apparatus according to the present invention for eliminating condensation from the outer wall thereof;

FIG. 2 is a plan view of a condensation sensor employed in the apparatus of FIG. 1; and

FIG. 3 is a schematic circuit diagram of the condensation eliminating apparatus employed in the system of FIG. 1.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

FIG. 1 shows a portion of a a refrigeration enclosure or cabinet. The enclosure defines or contains a zone or space 11 which is cooled by conventional refrigeration apparatus (not shown). The enclosure includes an inner wall 12 and an outer wall 13 which are separated by an insulating layer 15 in conventional manner. Conventional strip type anti-sweat heaters H1 and H2 are provided at spaced points along the outer wall 13-. When heaters H1 and H2 are energized, they heat the outer wall 13 to eliminate therefrom condensation which would otherwise be caused by the cooling of the outer wall due to heat transfer or leakage through the insulating layer 15.

The outer wall of the enclosure includes a recess 19 within which is mounted a condensation control assembly designated generally as 21. If desired, the recess may be covered by a grill to protect the assembly 21. Assembly 21 is mounted or positioned so as to be cooled with the outer wall 13 and preferably the insulation adjacent the assembly is, as illustrated, somewhat thinner than that separating the other portions of the inner and outer walls so that the assembly 21, in fact, reaches a temperature which is somewhat cooler than the temperature of the outer wall generally. In this way, if conditions develop which are conducive to the formation of condensation, the condensation will form first on the assembly 21.

As is illustrated in FIG. 2, assembly 21 incorporates a condensation sensor 24 which includes a pair of electrodes 25 and 27. Electrodes 25 and 27 may for example comprise areas of a conductive foil layer supported on an electrically insulating substrate 29. Such electrodes may be conveniently formed by selectively etching a metal foil covered substrate according to known printed circuit techniques. Electrodes 25 and 27 are thus supported on and bridged by the insulating surface of substrate 29. The electrodes are preferably shaped with complementary convoluted edges which define a tortuous gap between the electrodes. The substrate 29 is mounted on a casing 31 which may also serve as a housing for the electronic components described hereinafter. Mounted on casing 31 are a pair of terminals 33 and 35 by means of which the assembly 21 may be interconnected with the heaters H1 and H2 and a source of electric power.

Referring now to FIG. 3, the heaters H1 and H2 are connected in parallel with each other and are connected across a pair of AC. supply leads L1 and L2 through a circuit which includes the anode-cathode circuit of an SCR (silicon controlled rectifier) Q1. As is understood by those skilled in the art, SCR Q1 is a semiconductor current switching device which can control the flow of electric current to the heaters. The condensation sensor electrode 25 is connected directly to the anode terminal of SCR Q1 and the electrode 27 is connected to the gate or control terminal of the SCR through a diode D1 which is reverse biased when the SCR is reverse biased. As is understood by those skilled in the art, SCR Q1 is triggered into conduction on those A.C. half cycles when lead L1 is positive with respect to L2 if the resistance between electrodes 25 and 27 drops below a predetermined level which permits sufficient current to flow to the gate terminal of the SCR to trigger the SCR into conduction.

The operation of this apparatus is substantially as follows. If the refrigerator is operated in a relatively low humidity environment, the slight cooling of outer wall 13 caused by heat transfer through insulating layer 15 does not cause condensation to form on the outer wall 13. Under such circumstances the electrodes 25 and 27 are bridged only by the insulating substrate 29 and thus the SCR Q1 is not energized and the anti-sweat heaters H1 and H2 remain deenergized.

If, however, the refrigerator is operated in a high humidity environment, the slight cooling of the outer wall 13 produced by heat transfer through the insulation 15 may cause condensation to form on the outer wall 13. However, before any substantial sweating of outer wall 13 can occur, condensation on the sensor 24 causes moisture to bridge the gap between the electrodes 25 and 27 thereby lowering the resistance therebetween to a level which cause SCR Q1 to be triggered. Accordingly, SCR Q1 will conduct and thereby energize heaters H1 and H2 to eliminate condensation from the outer wall 13. It can thus be seen that the heaters H1 and H2 are automatically energized only when needed.

It should be noted that, if the condensation control apparatus of this invention is constructed as a unitary assembly as indicated at 21, only two connections need to be made to the assembly as may be seen from the circuit diagram of FIG. 3. While only half-wave power is applied to the anti-sweat heaters H1 and H2 in the embodiment illustrated, full-wave power may be employed by modifying the control circuitry to accommodate a triac which will conduct in either direction in place of SCR Q1. Other semiconductor current switching means may also be employed.

As various changes could be made in the above constructions without departing from the gist of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative.

In view of the above, it will be seen that the several objects of the invention are achieved and other advan tageous results attained.

What is claimed is:

1. In a refrigeration system including an enclosure having inner and outer walls separated by an insulating layer, means for cooling a space within said enclosure, and electric heater means for heating said outer wall to eliminate therefrom condensation caused by cooling of said outer wall due to heat transfer through said insulating layer; apparatus for selectively energizing said heater means comprising:

a semiconductor current switching means for controlling the flow of electric current to said heater means;

a sensor means including a pair of electrodes bridged by an electrically insulating surface, said sensor means being positioned relative to said enclosure to be cooled with said outer wall; and

means for energizing said semiconductor current switching means when the resistance between said electrodes falls below a predetermined level whereby, when the resistance between said electrodes is reduced by condensation of moisture on said surface, said heater means is energized by said semiconductor current switching means thereby eliminating condensation from said outer wall.

2. Apparatus as set forth in claim 1 wherein said current switching means is a triggerable semiconductor controlled rectifier.

3. Apparatus as set forth in claim 2 wherein said controlled rectifier includes a pair of terminals which are connected in series with said heater means and a control terminal for controlling conduction between said pair of terminals and wherein one of said electrodes is connected to one of said pair of terminals and the other of said electrodes is connected to said control terminal.

4. Apparatus as set forth in claim 2 wherein said rectifier is an SCR.

5. Apparatus as set forth in claim 4 wherein one of said electrodes is connected to the anode of said SCR and the other of said electrodes is connected to the gate of said SCR.

6. Apparatus as set forth in claim 5 wherein said other electrode is connected to the gate of said SCR through a diode which is reverse biased when the anodecathode circuit of said SCR is reverse biased.

7. Apparatus as set forth in claim 1 wherein said electrodes comprise areas of a conductive layer supported on an insulating substrate.

8. Apparatus as set forth in claim 7 wherein said electrodes have complementary convoluted edges defining a tortuous gap therebetween.

9. In a refrigeration system including an enclosure having inner and outer walls separated by an insulating layer, means for cooling a space within said enclosure, and an electric resistance heater for heating said outer wall to eliminate therefrom condensation caused by cooling of said outer wall due to heat transfer through said insulating layer; apparatus for selectively energizing said heater comprising:

an SCR the anode-cathode circuit of which is in series with said heater for controlling the flow of electric current therethrough; sensor means including a pair of electrodes having complementary convoluted surfaces supported on an electrically insulating substrate, said sensor means being supported relative to said enclosure to be cooled with said outer wall, one of said electrodes being connected to the anode of said SCR; and

means including a diode for connecting the other of said electrodes to the gate of said SCR whereby, when the resistance between said electrodes is reduced by condensation of moisture on said substrate between said electrodes, said heater is energized by said SCR thereby eliminating condensation from said outer wall.

References Cited UNITED STATES PATENTS MEYER PERLIN, Primary Examiner.

US. Cl. X.R. 

